AI agents use update_active_context to create or update resources in Memory Bank MCP — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Memory Bank MCP environment.
This tool modifies the active context file, which is a write operation. It is reversible (can be updated again) and does not permanently delete data, making it Write rather than Destructive.
From the tool's definition Tool name 'update_active_context' and description 'Update the active context file' indicate modification of data. The verb 'update' is a classic write operation that creates or modifies data reversibly.
Documented attack patterns abuse exactly the kind of access update_active_context gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Memory Bank MCP, and nothing reaches the server without passing your rules. This is the rule we recommend for update_active_context:
{
"version": "1",
"default": "deny",
"tools": {
"update_active_context": {
"limits": [
{
"counter": "update_active_context_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}update_active_context stays usable, but capped — an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.
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Update the active context file. It is categorised as a Write tool in the Memory Bank MCP MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Memory Bank MCP server in PolicyLayer and add a rule for update_active_context: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches Memory Bank MCP. Nothing to install.
update_active_context is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.
Yes. Add a rate_limit block to the update_active_context rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.
Set action: deny in the PolicyLayer policy for update_active_context. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.
update_active_context is provided by the Memory Bank MCP server (movibe/memory-bank-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Memory Bank MCP, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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15 Memory Bank MCP tools catalogued and risk-classified — across an index of 43,000+ MCP servers.